The Obama administration is beginning an aggressive new effort to foster equity in criminal sentencing by considering clemency requests from as many as thousands of federal inmates serving time for drug offenses, officials said Monday.

The initiative, which amounts to an unprecedented campaign to free non­violent offenders, will begin immediately and continue over the next two years, officials said. The Justice Department said it expects to reassign dozens of lawyers to its understaffed pardons office to handle the requests from inmates.

“The White House has indicated it wants to consider additional clemency applications, to restore a degree of justice, fairness and proportionality for deserving individuals who do not pose a threat to public safety,” Attorney General Eric H. Holder Jr. said Monday. “The Justice Department is committed to recommending as many qualified applicants as possible for reduced sentences.”

Holder has announced a series of initiatives to tackle disparities in criminal penalties, beginning in August when he said low-level, nonviolent drug offenders with no connection to gangs or large-scale drug organizations would not be charged with offenses that call for strict mandatory sentences. He has traveled across the country to highlight community programs in which nonviolent offenders have received substance-abuse treatment and other assistance instead of long prison sentences.

Underlying the initiatives is the belief by top Justice Department officials that the most severe penalties should be reserved for serious, high-level or violent drug traffickers. On April 10, after an endorsement from Holder, the U.S. Sentencing Commission — the independent agency that sets sentencing policies for federal judges — voted to revise its guidelines to reduce sentences for defendants in most of the nation’s drug cases.

In the meantime, however, thousands of inmates are still serving federally mandated sentences that imposed strict penalties for the possession of crack cocaine. The Fair Sentencing Act, which President Obama signed in 2010, reduced the disparity between convictions for crack and powder cocaine, and Obama has called sentences passed under the older guidelines “unduly harsh.” The law also eliminated the five-year mandatory minimum sentence for the simple possession of crack cocaine.

“There are still too many people in federal prison who were sentenced under the old regime — and who, as a result, will have to spend far more time in prison than they would if sentenced today for exactly the same crime,” Holder said Monday. “This is simply not right.”

For about two decades, strict sentences were imposed on offenders convicted of trafficking or possession with intent to traffic crack cocaine in the belief that the substance was more addictive than powder cocaine, inexpensive and linked to violent crime.

But in 2002, the sentencing panel found that sentencing guidelines were based on misperceptions about the relative dangers of crack cocaine compared with other drugs. The commission also found that the disparity had created a racial imbalance in which harsh sentences had been disproportionately imposed on minorities, particularly African Americans.

In December, Obama commuted the sentences of eight inmates serving long prison terms for crack-cocaine convictions handed down before the 2010 law was passed. Six of the eight were serving life sentences, including two who had not previously been convicted. Each of the eight had served more than 15 years for a crack offense.

Under the 2010 law, the same people would have received shorter prison terms and, in some cases, completed their sentences.

On Wednesday, Deputy Attorney General James M. Cole is expected to announce details about the new criteria the Justice Department will use in considering clemency applications and how the department plans to review those applications.

The department has asked the American Civil Liberties Union and other nonprofit groups to help identify candidates for clemency. Some of those groups are likely to help inmates submit the necessary paperwork.

“Once these reforms go into effect, we expect to receive thousands of additional applications for clemency,” Holder said. “And we at the Department of Justice will meet this need by assigning potentially dozens of lawyers — with backgrounds in both prosecution and defense — to review applications and provide the rigorous scrutiny that all clemency applications require.”

White House Counsel Kathryn Ruemmler said Obama has directed the department to improve its process for clemency recommendations and try to recruit more applicants from the federal prison population of low-level drug offenders.

In a speech at New York University’s law school last week, Ruemmler said clemency is an important “fail-safe mechanism” in the criminal justice system.

“When a worthy candidate runs out of other options,” she said, “the president has the power to correct an injustice that no one else has.”